MI60 Clone

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Mikka
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Re : MI60 Clone

Message non lu par Mikka »

Hi,

Don't worry, you'll probably fixe your problems.

For the BIAS you can try to increase the R25 value from 18k to 22k or 27k.
Th hum can be creat by the overload of the power tranny because the too higher BIAS but your layout seems to be not really the best.
Your heater wires are not in the best place.
It's usually better too pass them Along the frame under the speaker jaks and well twisted.

Hope this helps you.

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a-wai
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Re : MI60 Clone

Message non lu par a-wai »

Hi !

Are the 90mA measured for only one tube or for both ?
Regarding the buzz, it's generally caused by a bad wiring (maybe a ground loop, or the heater wires getting too close to signal wires)

By the way, double posts are prohibited here, and you will probably have your ass kicked by vitriol82 for this ;)
Here is how you should do to :
1. Edit you last post and copy all of its content
2. Delete it using the Image button
3. Post a reply, paste your first post and add whatever you want
4. You're done :good:

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theleftfoot
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Re : MI60 Clone

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okay...i removed the resistor....and now i'm in the ball park....bias is about -37.2V and the current about 39 mA...

i drilled the heater cable and cleaned the amp up...


but unfortenatly the buzz is still hear... :cry:

AMP BUZZ Soundfile here --> http://www.cshare.de/file/90155b2a5be48 ... 59e75a449a

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vitriol82
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Re : MI60 Clone

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Hello,

I think that you don't have the good PT, too low, this one can generate hum by magnetic saturation.

Have you the datasheet of this PT? It's necessary to have a good analysis of this one.

I could give you a better answer after cheking this informations.
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theleftfoot
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Re : MI60 Clone

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sorry...i d'ont have more information about the PT....as i say!

i took this out from a hybrid amp with 1 12ax7 an 2 6c6 tubes....

what about the wiring? can i put some signal wires up on the same line with the ground wires?

i try to put of one pre-amp tube...

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vitriol82
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Re : MI60 Clone

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Hello , 6C6 tubes are not power BF pentode, only the heater is 300 mA per tube, heather power needed by the old amp was 300+300+300 = 900 mA.
http://www.mif.pg.gda.pl/homepages/fran ... /6/6C6.pdf

For the MI60 heater power minimum needed is :

750 mA for each EL34 and 300 mA for each 12AX7

Your hum is for me generated by the heater witch must be under 6V (with all tubes installed), minimum required for a good tube's work.

Could you check the voltage of the filaments with all tubes installed?
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theleftfoot
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Re : MI60 Clone

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no, the heater with all tubes in is 6.83V!

i meassed around with the bias current...when i put the bias current down to 10 mA the buzz goes a little bit gone....still here but not to loud....

then i checked the bias circuit and find out that i don't have a resistor parallel to the cap! thats mean that i have some niggles on the sinus wave...

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vitriol82
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Re : MI60 Clone

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??? R25 is not parallel to C16 ???

6.83V for heater? Strange your story....it seems to have no consumption, so and without tubes what is the heater voltage?
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theleftfoot
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Re : MI60 Clone

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hmm....i must check the bias circuit again....think i have a error there....give me 20 min

EDIT MODO

okay...i've done the C700 bias circuit like this --> http://gilles.thebault.free.fr/IMG/jpg/ ... iginal.jpg....the volltage is okay...but the current a way to high with near 100 mA...my bias pot is 100k ....after the rectifier i have across 37 VDC..

can you adjust the circuit for me ....?

raffa

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vitriol82
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Re : MI60 Clone

Message non lu par vitriol82 »

The general rules of this forum don't agree with the multi posts, you must use the EDIT button to write your new message.

I've cleaned this one but the next time you have to do this job alone, ifont, there will be be not answer along the double post exist.

Regarding the schematic, the pot must be installed instead R23 but I don't understand "rectifier", you must have only one diode.

There is a little difference beetwen the schematic and the layout

Just see here to understand

http://gilles.thebault.free.fr/MI60/MI60bias.gif
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warteko
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Re : MI60 Clone

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Hi all friends !

Didn't anyone spot the "light"(to not say "poor") twisting of the heaters'wires ? Isn't it a potential problem ?

Warteko

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theleftfoot
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Re : MI60 Clone

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yes, i changed it allready....pics will follow

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warteko
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Re : MI60 Clone

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Otherwise, I have found the overall job quite OK.

Sure will end in a son of a gun cool amp!
What kind of axe do you want to plug in it, and what style of music do you intend to treat it ?

Warteko

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theleftfoot
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Re : MI60 Clone

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merci beaucoup.... i use epi les paul studio, and telecaster...sometimes a strat...we play alternative brit sound...some sort of the martins! yeah TBO nice sounds! 8)

back to topic...how can i decrease the current on this amp? bias okay...but the current!

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charpy
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Re : MI60 Clone

Message non lu par charpy »

for the same plate current the bias voltage varies between different tube even for the same brand. then you need to adjsut the bias voltage for your tube and each time you change the tube.

don't focus on the grid voltage it doesn't mean anything. the only thin to set precisely is the plate current.

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